Bump pillow from 4.3.0 to 6.2.0

Bumps [pillow](https://github.com/python-pillow/Pillow) from 4.3.0 to 6.2.0.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@4.3.0...6.2.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,7 +1,7 @@
 tflearn==0.3.2
 numpy==1.16.5
 gym==0.9.4
-Pillow==4.3.0
+Pillow==6.2.0
 psutil==5.6.3
 statsmodels==0.10.1
 tensorflow==1.12.0